Vacuum-tube electrode and process of operating same.



W. I). COOLIDGE. VACUUM TUBE ELECTRODE AND PROCESS OF OPERATING SAME.

APPLICATION FILED SEPT-1. I912.

Patent d Oct 26,1915.

Witnesse Inventor:

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WILLIAM D. COOLIDGE, OI? SCHENECTADY, NEW YORK, ASSIGNOB T GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW-YORK.

vacuum-roan nnnc'rnonn AND rnoonss or ornnafrme same.

Specification of Letters Patent. Patented Oct, 26, 1915.

Application filed September 7, 1912. Serial No. 719,218;

To all whom it may concern:

Be it known that I, WILLIAM D. Coonioos, a citizen of the United States, residing at Schenectady, in the county of Schenectady and State of New York, have inventc certain new and useful Improvements in Vacuum-Tube Electrodes and the Process of Operating the Same, of which the following is a specification.

The present invention relates to the operation and structure of high powered Rtintgen or similar vacuum tubes. In apparatus of this nature, large amounts of energy are disengaged in a short time. In order to increase the capacity of the electrode for taking care of this energy, the body of refractory metal, for example, platinum, which serves as a target at the focal spot of the cathode rays, has been placed in heatconducting relation with a large mass of copper, the function of which is to act as a heat storage reservoir and prevent the temperature of the refractory metal from rising to a point where appreciable evaporization takes place. In case the refractory metal is ut in direct contact with the copper, the cat conductivity to the latter is sufficient to cause such a rapid removal of heat that a large portion of the refractory metal is at a low temperature even after the focal spot has been brought to its maximum temperature. In the case of some refactory metals, such as tungsten, the strains due to the unequal temperatures are apt to crack the metal.

The present invention consists in so limiting the heat conductivity between the refractory metal and the heat reservoir that the temperature of the former shall quickly rise to and keep above a certain minimum temperature. This construction is particularly valuable in the case of metals, such as tungsten, which at low temperatures are brittle and therefore likely to be cracked under the influence of the forces of heat expansion incident to the cathode ray bombardment.

Figure 1 shows partly in section a target or anticathode illustrating one embodiment of my invention; Fig. 2 is a longitudinal section of an alternative structure, and Fig. 3 is a cross-section of the same.

As shown in Fig. 1, a disk, or plate 1, of tungsten, preferably malleable or ductile tungsten, is supported in heat-conveying relation by a stem 3 to a holder 2 consisting of copper, silver or the like. The stem 3 preferably also consists of copper, which can be integrally attached to the tungsten by heating copper in; contact with the tungsten in a vacuum to a temperature considerably above the melting point of copper, say 1400 C., as described 1n my copending application, Serial No. 685,113, filed March 20, 1912.

According to another method, the copper is first degasified by treatment with boron suboxid, or oxidizable boron compound, and then brought in a molten condition into contact with the tungsten. This method as described in my copending application, Serial No. 716,206, .filed August 21,1912, retains the characteristics of wrought tungsten as the tungsten is not overheated. When thus attached by either method, the stem may be trimmed down on a lathe, or in any other way to make a tight fit 1n the recess in the copper block 2. Its height is ad]usted so that a space remains between it and the co per block as indicated.

some cases it is desirable tosurround a body of tungsten with copper' or other heat-storin material. Suchaconstruction is illustrated in Fig.2. In this case, the copper block 4 is tubular, one side of the tube being split at the point marked 5 in Fig. 3. The body of tungsten 6 is clamped in 1position in the copper block by a screw 7 T e mannor of holdin the body of tungsten is best illustrated in ig. 3, which is a cross-section on the lines 3, 3 of Fig. 2. In this case the working face of the tungsten body is also separated by a clearance space from the heat storing mass, and the connecting shank is constituted by the section of the tungsten body intermediate between the working face and the clamped surface of said body. In this construction it is obvious that the conduction of heat from the working face of the body of tungsten 6 takes place through a relatively lon path, as contact between the tungsten an the copper is made at a point remote from the region where the heat generated.

When an electrode constructed as above described is suitably mounted as target or anti-cathode in a Rtintgen ray tube, the disk of tungsten operates as the active part of the electrode, and, because of a transfer of A through a path of lower heat conductivity than a direct thermal contact immediately adjoining the heated zone the tungsten body will operate at a fairly high temperature at which the metal possesses a high degree of pliability. This temperature may be as low as 300-400" C. The presence of the large mass of copper with its heat storage capacity will permit the tungsten disk to operate at higher current densities without melting than would otherwise be possible.

At the beginning of the o eration, a small amount of current is put t rough the tube to warm up the target to the required temperature. The current strength may then be increased to the full capacity of the tube, the heat bein removed at he required limited rate by t e copper as described.

\Vhile I have described m invention with reference to a particular orm of vacuum tube target, or electrode, I desire it to be understood that it is equally applicable to other forms.

NVhat I claim as new, and desire to secure by Letters Patent of the United States, is

1. A Ront en my target comprising a mass of meta of good heat conductivity, a tungsten body spaced apart from said mass near the working face of said tungsten body, and a heat conductive connection between said mass of metal and the tungsten body, said connection affording a slower transfer of heat than direct thermal contact between the mass of metal and the tungsten bod 2. An X-ray target comprising a bod; of refractory metal arranged to receive the cathode rays and a body for receiving and storing heat, said bodies being spaced apart at the discharge-receivin face of the refractory metal body but oined by a shank affordin a path of lower heat conductivity than a tired; thermal contact between the heat receiving layer of the refractory metal and the heat storing body, so that the tungsten body may be maintained at a high temperature during operation substantia ly uniform throughout.

3. An X-ray electrode comprising aholder tion adjoining the heated zone,

of copper, and a body of malleable tungsten, the copper and tungsten being spaced apart at a region adjoining the working face of the tungsten body, but connected through a shank affording transfer of heat at a rate materially less than a close thermal connecso that the temperature of the tungsten body may be maintained throughout materially above the temperature of the copper mass.

4. An X-ray target comprising a body of malleable tun ten, a body of copper and a stem of meta smaller in cross-section than said tungsten body connecting said bodies, the tungsten body and copper body being otherwise separated by a space.

5. The method of operating a Rontgenray target comprising a refractory metal body which is brittle below a predetermined temperature which consists in first gradually raising the temperature of said body by a smal heated to a temperature at which it is pliable and subsequently operating with a full energy input.

6. The method of operating a tungsten Rontgen tube target which consists in first gradually raising its tem erature to a value at which it is pliable, t en increasing the input of energy to the normal operating capacity and carrying away heat at a rate proportioned to at least maintain said temperture and sufiicient to prevent undue heatmg.

7. An X-ray target comprising a disk of tungsten, a copper holder, and a stem of metal of materially smaller cross-section than said tungsten and cop er holder joinmg said bodies, said stem a ording the sole heat conductive "connection between said bodies.

In witness whereof, I have hereunto set my hand this 6th day of September, 1912.

WILLIAM D. COOLIDGE.

Witnesses BENJAMIN B. HULL, Hanan Onroan.

Copies o1 this patent may be obtained for five cents each, by addressing the Oommisstoner 0: Patents. Washington, D. 0."

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